1. Field of the Invention
This invention relates generally to a textile-reinforced, elastomeric polyurethane articles for dynamic applications, more particularly to a power transmission belt with a plasticized polyurethane/urea elastomer and carbon fiber tensile cord, and specifically to an improved polyurethane/urea elastomer composition which improves flex fatigue resistance of carbon fiber tensile cord in polyurethane belts.
2. Description of the Prior Art
It is generally known that certain additives, known as plasticizers or diluents, when added to polyurethane prepolymers will reduce the viscosity of these prepolymers. Unfortunately, a simultaneous effect of these additives is to significantly reduce certain cured properties of the polyurethane elastomer such as hardness, tensile modulus, and tear strength.
U.S. Pat. No. 5,907,014 discloses polyurethane prepolymers with improved wettability without sacrificing physical properties. Prepolymers with dibasic esters, preferably aliphatic dialkyl esters where the alkyl group is C1 to C7, and diamine or polyol curatives are applied to one or more fabric plies and are subsequently cured at the appropriate temperature and time to create a finished product, i.e., a conveyor belt.
U.S. Pat. No. 6,964,626, the contents of which are hereby incorporated herein in its entirety, discloses improved polyurethane/urea elastomers having high temperature stability to about 140-150° C. and low temperature flexibility at about −35-(−40)° C., for use in dynamic applications. These elastomers are useful for application in belts, specifically in automotive timing or synchronous belts, V-belts, multi-V-ribbed or micro-ribbed belts, flat belting and the like. The polyurethane/urea elastomers are prepared by reacting polyisocyanate prepolymers with symmetric primary diamine chain extenders, mixtures of symmetric primary diamine chain extenders and secondary diamine chain extenders, or mixtures of symmetric primary diamine chain extenders and non-oxidative polyols, which are all chosen to eliminate the need for catalysts via standard molding processes, and to improve phase separation. The polyisocyanate prepolymers are reaction products of polyols which are nonoxidative at high temperatures, such as polycarbonate polyols, polyester polyols, or mixtures thereof, with organic polyisocyanates which are either compact, symmetric and aromatic, such as para-phenylene diisocyanate, 1,5-naphthalene diisocyanate, and 2,6-toluene diisocyanate, or are aliphatic and possess trans or trans,trans geometric structure, such as trans-1,4-cyclohexane diisocyanate and trans,trans-4,4′-dicyclohexylmethyl diisocyanate.